The present invention relates to a method for the correction of a message to be transmitted between a transmitter and a receiver that are distributed on an information transmission line of an installation supplied by the mains supply system.
The invention can be applied with particular advantage, but not exclusively, to the field of the management of computerized home automation systems.
Computerized home automation systems generally comprise a plurality of appliances and devices distributed on an information transmission line. These may be domestic appliances as such, for example television sets, refrigerators, washing machines, radiators etc. or, again, one or more control stations designed to receive instructions or information elements pertaining to the operation of the other appliances and devices. These instructions are, for example, "OFF" or "ON" commands coming from a user or from the appliances and devices themselves. In turn, the control station or stations send commands to the other appliances and devices of the installation in the form of messages that make it possible to obtain the desired modifications of operation.
To send these commands, different types of media are commonly used for the information transmission line, for example carrier current, coaxial cables, twisted pairs, infrared radiation and RF channels as well as optic fibers, ultrasound etc. Although its application is very general, the invention relates more particularly to carrier current which is the preferred medium used for home automation installations.
The installation envisaged here may be of the centralized intelligence type, with a control station exchanging messages with other devices that play the role of slave stations. In a distributed intelligence type of installation, each device can play the role of master or slave by self-programming without going through a control station which, for its part, only listens to the messages.
Until now, the appliances and devices intended for integration into a home automation installation have been designed by manufacturers to work in a given configuration of reception defined by a control message transmission rate that depends on the type of device concerned. It is thus that heating appliances can work at a relatively low rate of 300 baud, this rate being, however, substantially insufficient for lighting appliances which require a transmission rate that is substantially higher, at least 2400 baud.
In order to enable these different devices and appliances to coexist on one and the same information transmission medium, steps towards achieving compatibility were begun in 1991, the aim being to lay down a signal transmission rate of 1200 baud.
However, it must be expected that, in the relatively near future, devices working at higher rates of information transmission, 2400 baud for example, are likely to be connected to installations that comply with the prevailing standard.
This is why, in order to obtain the fullest possible compatibility, the trend is towards the development of devices that can send and receive messages at a minimum of two information transmission rates. A system for the transmission of data in an installation of this type, comprising devices such as these, is described in the European patent application No 93401231. 1, which is hereby incorporated by reference.
Furthermore, home automation applications may be the site of numerous disturbances likely to affect the transmission of the messages moving along the lines. These disturbances are of two types, i.e. 1) recursive parasitic pulses produced by devices such as motors, glow-discharge tubes and induction furnaces and, 2) variations in the line impedance of the installation, through resistive, capacitive or inductive causes, leading to an attenuation of the amplitude of the bits while they are being propagated between a transmitter and a receiver that are relatively distant from each other on the transmission line. In both cases, the receiver instrument is in no position to understand the messages sent to it, either because the bits that form these messages are deformed by the parasitic phenomena or because they arrive with an excessively low amplitude.